Cavosonstat (N91115) for Cystic Fibrosis

Cavosonstat (N91115) was an experimental therapy being developed by Nivalis Therapeutics. Its primary mechanism of action was to inhibit the S-nitrosoglutathione reductase (GSNOR) enzyme and to stabilize cystic fibrosis transmembrane regulator (CFTR) protein activity. A press release published in February announced the end of research for this therapy in cystic fibrosis (CF) patients with F508del mutations. The drug, which did not meet primary endpoints in a Phase 2 trial, had been referred to as the first of a new class of compounds that stabilizes the CFTR activity.

History of cavosonstat

During preclinical studies, N91115 (later named cavosonstat) demonstrated an improvement in cystic fibrosis transmembrane regulator (CFTR) stability.

Phase 1 study was initiated in 2014 to evaluate the safety, tolerability, and pharmacokinetics (how a drug is processed in the body) of the drug in healthy volunteers. Later that year, the pharmacokinetics of the drug were assessed in another Phase 1 trial involving CF patients with F508del mutation suffering from pancreatic insufficiency. Results were presented a year later by Nivalis, revealing good tolerance and safety in study participants.

A second, much smaller Phase 2 study (NCT02724527) assessed cavosonstat as an add-on therapy to ivacaftor (Kalydeco). This double-blind, randomized, placebo-controlled study included 19 participants who received treatment with cavosonstat (400 mg) added to Kalydeco or with placebo added to Kalydeco. The primary objective was change in lung function from the study’s start to week 8. However, the treatment did not demonstrate a benefit in lung function measures or in sweat chloride reduction at eight weeks (primary objective). As a result, Nivalis decided not to continue development of cavosonstat for CF treatment.

The U.S. Food and Drug Administration (FDA) had granted cavosonstat both fast track and orphan drug designations in 2016.

How cavosonstat works

The S-nitrosoglutathione (GSNO) is a signaling molecule that is present in high concentrations in the fluids of the lungs or muscle tissues, playing an important role in the dilatation of the airways. GSNO levels are regulated by the GSNO reductase (GSNOR) enzyme, altering CFTR activity in the membrane. In CF patients, GSNO levels are low, causing a loss of the airway function.

Cavosonstat’s mechanism of action is achieved through GSNOR inhibition, which was presumed to control the deficient CFTR protein. Preclinical studies showed that cavosonstat restored GSNO levels.

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